1. Field of the Invention
The present invention relates to an image forming apparatus such as an electronic copying machine and, more particularly, to an image forming apparatus having an automatic original feed/discharge unit.
2. Description of the Related Art
For example, a conventional plain paper copier copying machine includes an original table surface (normally a glass platen) and an exposing means for scanning an original on the original table surface. A main body of the PPC copying machine incorporates image forming process means for charging, exposure, development, cleaning, fixing, and the like. Various types of conventional copying machines each having automatic original feed/discharge unit (i.e., an automatic document feeder) are commercially available. This original feed/discharge unit normally comprises a feed table for supporting originals prior to scanning, a discharge table for supporting the originals after scanning, and an original feeding means for feeding the originals one by one onto the original table surface and discharging the originals one by one onto the discharge table after scanning. An endless conveyor belt traveling while contacting with the original table surface is frequently used as the original feeding means. This endless conveyor belt also serves as a platen sheet for holding the original onto the original table surface. A new conveyor belt is white as a whole.
The conveyor belt must be arranged in a long conveying path from the feed table to the delivery table and must have a width large enough to cover the entire original table surface. For these reasons, in a conventional automatic feed/discharge unit, a considerably large endless belt and a large belt drive mechanism are required. The belt, the drive mechanism, and the like are housed in a unit cover which is pivotally mounted on a main body of the image forming apparatus. For this reason, the cover is large in size and heavy, and cannot be easily opened/closed. In addition, an implementation for stabilizing the travel state of the belt is required, resulting in high cost.
The belt is driven endlessly while slidably contacting with the original table surface and the adjacent members. For this reason, the belt drive mechanism must have a larger drive force. Even if the belt is white when it is new, the belt is easily contaminated in an initial period of use. When the belt is greatly contaminated, sharpness of the resultant image tends to be degraded.